Long-term spatial dynamics in an old-growth deciduous forest

In 1926, 1976, and 1986 stems (greater than or equal to 10 cm diameter at 1.37 m (dbh)) were measured and mapped in a 4 ha interior study area on the Davis-Purdue Research Forest in east-central Indiana. Spatial pattern type was determined using the Clark and Evans's index, and Ripley's L function. The G function was used to examine spatial dispersion at intertree distances (< 20 m). Spatial pattern of combined size classes shifted from weakly non-random in 1926 to uniform in 1976 and 1986. Neighborhood density was depressed for 2 m in 1976 and 5 m in 1986. Peak in neighborhood density at 6 m suggested trees were spaced 6 m apart. Subcanopy (10-25 cm dbh) tree spatial pattern shifted from aggregated in 1926 to uniform in 1976. The spatial pattern of canopy (> 25 cm dbh) trees was uniform between 1926 and 1986. Density-dependent mortality and ingrowth processes are maintaining uniform spatial distributions. Initial neighborhood tree distribution was higher around trees which died in the periods 1926-1976 and 1976-1986 than for contemporary survivors, i.e. trees which survived this period had fewer neighboring trees within 6 m at the beginning of the period than did trees which died. The higher initial neighborhood densities around mortality trees than survivors supports density-dependent mortality. Ingrowth was inhibited in a 6 m zone proximite to established trees for both the 1926-1976 and 1976-1986 periods.